This invention relates to grounding of electrical systems in structures such as airplanes.
There has been a long-standing problem concerning installation of grounding studs on commercial aircraft. Threaded fastener studs are used on aircraft structure to establish a ground interface for electrical systems wiring to the aircraft""s structural ground plane. But, during assembly or maintenance procedures, the fastener-studs can loosen and require retorqueing. Because of the wiring complexity and structural interferences common in aircraft manufacturing, access to the backside of the ground plane structure for restraining a stud""s rotation during retorqueing is a difficult task. Also, simple wire terminal removal or replacement procedures can result in the stud-terminal-retaining nut assembly to come loose and spin in place. This can tear off the wiring terminals or result in other damage.
These problems significantly impact commercial aircraft manufacturing costs and schedules.
The invention provides a method and an apparatus for producing a grounding path on a structure, which is particularly advantageous for commercial aircraft manufacturing processes. In a preferred embodiment, a method for providing an electrical ground path on a structure, such as a grounding plate on a commercial aircraft, includes pre-drilling holes in the structure with standard spacing between a grounding stud and a retaining rivet, inserting a stud (with a pre-drilled retaining rivet hole to match standard spacing) through its respective mounting hole in the structure, aligning holes and riveting the leg of the grounding stud to the structure using a oneside installed pop rivet through the pre-drilled holes, installing a washer over the ground stud, installing a jam nut to the wire terminal side of the structure and tightening the jam nut to prescribed torque, installing wire terminals as required, installing a washer over the wire terminals, installing a lock nut, and tightening the lock nut to prescribed torque.
In a preferred embodiment, the stud includes a head or spade portion extending substantially perpendicular to the threaded portion of the stud and adapted for receiving a rivet (for example, a pop rivet). An apparatus according to a preferred embodiment includes a stud having a head which includes a spade disposed substantially perpendicular to the threaded stud with a hole therethrough adapted for receiving a rivet.
In a preferred embodiment, the stud acts as a self-retaining grounding stud-fastener. The head of the stud is enlarged to produce a flat spade head oriented at a right angle to the threaded shank portion of the stud. Holes are pre-drilled in the structure and stud head at a standard spacing to match the distance between the centerline of the stud shank and the retaining rivet to ensure alignment during assembly. The head receives a rivet (preferably from the wire terminal side) to prevent rotation of the ground stud during nut installation, removal, replacement, or retorqueing. The ground stud head is designed with enough edge margin from the pre-drilled rivet hole to allow for hole enlarging to accept a larger rivet if damage is done to either rivet hole and rework is required.
This solves a long-standing problem in aircraft manufacture, where small enclosed spaces and complex wiring paths and structures make it difficult to access both sides of a grounding plate that incorporates grounding studs that can spin. Once installed, a preferred embodiment of this invention will allow installation, servicing, and replacement of wiring from one side of the grounding plate.